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Guest Column: A Dash of Chance

At last, scientists have begun to decipher that most thrilling moment of urban predation: you fix the cockroach in your sights; without taking your eye off him, you slowly remove one shoe; and you stalk, ever so stealthily, toward your quarry.

What you long to know, of course, is which way he will dash. But what scientists have discovered, I regret to report, is that the roach defies such divination. Just as the deadly heel swings down, the roach will make a sudden rotation, then scurry, and that quick swivel is his vital secret.
The turn will position him in one of four orientations: he’ll point himself roughly 90, 120, 150 or 180 degrees away from the wind your shoe creates. But which of the four will it be? Aye, there’s the rub. For that, it turns out, is highly unpredictable.

This study intrigued me, not just because the scientists seemed so heroically curious, startling five famous roaches 90 times each, but also because of the way their results relate to our idea of adaptation. Our favorite icons of adaptation seem generally to feature precise and elegant fit between form and function: the hummingbird’s long tongue reaches into the equally long corolla of a flower, simultaneously feeding the bird and fertilizing the plant; the coloration of a moth precisely matches the tree bark on which it rests, rendering the insect almost invisible.

And behaviors, too, can seem perfectly tuned: that hummingbird is in all likelihood what evolutionary ecologists call an optimal forager, consistently making decisions that will maximize the rate at which it ingests energy; and even the dull moth alights reliably on just the right background.

But the cockroaches got me thinking about cases in which adaptation calls not for perfect tuning or precise definition, but rather for something more like their opposite: an absence of definition, a dash of chance. If that roach were always to flee in one predefined direction, its predators would soon catch on. You’d know exactly where to aim the heel. But in choosing his path at random, the roach achieves an adaptive unpredictability.

Once you start looking for this sort of thing, you find it everywhere. When some animals are searching for food, they make occasional random turns, which take them into fresh territory, and also happen to make their paths look like certain kinds of random walks — probabilistic outcomes for which mathematicians have special names.

And evidently, among some species of prey, the response to an oncoming predator is to do as much unpredictable, weird and pointless stuff as possible, increasing the probability that the attacker will a) be totally confused, b) decide that messing with such a crazy character is too risky, or c) infer that the prey is infected with a strange — and possibly transmissible — parasite. (O.K., I made that last one up, but I bet we could find an example.)

Even among the microbes, which are so streamlined they sometimes seem more like tiny machines than organisms, we can find adaptive roles for randomness. Take, for instance, Trypanosoma brucei, the parasite that causes sleeping sickness, a chronic disease that can last for years. What makes T. brucei so difficult for the immune system to track down and eliminate is that the microbe keeps swapping out the molecules that encrust it, and each new disguise is entirely unpredictable.

Here’s how it works. T. brucei stores in its genome about a thousand different versions of the gene that codes for a protein called VSG. If we think of VSG as a tiny plate of microbial armor, then each gene for it is like a distinctive die, which stamps out a plate embossed with a unique design. At any given moment, the microbe manufactures only one version of its plate mail.

But which one? That depends on which of those thousand different genetic dies happens to sit in a certain location in the genome — think of it as the microbe’s only forge for making VSG. And since the T. brucei genome is constantly shuffling around those thousand genes, swapping their locations at random, there’s no telling which die will end up in the forge.

Intriguingly, the immune system uses a similar strategy to make the antibodies that seek out and mark T. brucei for destruction. For an antibody to succeed in its task, it must be imprinted with a design that fits perfectly over the bas-relief on the microbe’s armor. But since that relief changes frequently and unpredictably, the immune system must shuffle its own dies in and out of its forge, making a variety of antibodies until it finds just the right imprint. The patient’s battle with sleeping sickness is essentially a race to see whose shuffling works faster.

On both sides of the race, extra novelty is introduced through high rates of mutation: Even as the genes are shuffled, small, unpredictable changes hit the DNA here and there. And if an antibody’s imprint happens to fit the microbial armor almost exactly, the immune system will subject the gene for that particular imprint to an extremely high rate of mutation, accelerating the search for exactly the right fit.

Here, however, we must make a careful distinction.

Hypermutation of antibody genes is a clear example of chance harnessed by an evolved system. But most other kinds of mutation — those outside of the immune system’s highly variable genes — cannot qualify as randomness that the organism uses to its own advantage. The vast majority of mutations are harmful, and the apparatus that handles genes in fact goes to great lengths to prevent mutations from ever occurring. Yes, those rare beneficial mutations are accumulated by natural selection to fashion adaptations. But that’s something different from what’s going on in the immune system. There, mutation is harnessed by the individual; elsewhere, it is harnessed only by natural selection itself.

That distinction seems clear enough. And yet, when we turn our attention to another form of genetic novelty — not mutation, but sex — the line begins to blur.

From an evolutionary point of view (and perhaps from several others, as well), exactly what sex does for us is a big, complicated question. There is little doubt, however, that sex introduces a lot of chance into the reproductive process. If you clone yourself, you know exactly what genome your offspring is going to have: yours. But when you reproduce sexually, you pass along only half your genome — and which half is mostly a matter of chance. As for the other half of your offspring’s genetic endowment, to control that, you can only choose your mate carefully, and hope for the best.

Which brings us back to that moment of fertilization — the hummingbird hovering over its flower. It seems to me that, wrapped up in such icons of adaptation is a view of evolution by natural selection as a process that drives out randomness and disorder. And randomness and disorder, for their part, are seen as the dangerously destructive forces that invade whenever adaptation can’t hold them at bay.

That’s mostly right, I think. Even in our examples of chance harnessed for adaptive purpose, the bridled force remains alarming unruly. In the T. brucei genome, over 90 percent of genes coding for VSG are dysfunctional. They’ve had holes poked in them by mutation, or have been accidentally chopped apart by the very shuffling process that sustains the microbe’s variation. And of course, the genetic shuffling of sex, too, comes with many significant costs and risks.

And yet, in spite of all the dangers, evolution by natural selection so often invites chance in from the wilderness. Beside the hovering hummingbird, therefore, we ought to hold up the dashing roach, the wandering forager, even the protean T. brucei. For they all remind us that precision and order are not always favored over an unpredictable or creative disorder.

When Darwin first described evolution by natural selection, a critic, unhappy with the role of chance in the process, called it “the law of higgeldy-piggeldy.” As it turns out, evolution not only crafts adaptations of astonishing elegance and intricacy, but also stables a certain amount of “higgeldy-piggeldy.”

A word about my use of the words random and randomness. I use them in the sense of a “random variable” in probability. A random variable is not necessarily perfectly unpredictable: it can be more likely to take some values than others; it can be confined to a certain range.

For a nice paper on co-adaptation between hummingbirds and flowering plants, see V. Grant and E.J. Temeles (1992) Foraging ability of rufous hummingbirds on hummingbird flowers and hawkmoth flowers. PNAS 89: 9400-4.

The story of moth crypsis can be found in many undergraduate textbooks on biology and evolution. A starting point to read about hummingbirds as optimal foragers is R.D. Montgomerie et. al. (1984) What do foraging hummingbirds maximize? Oecologia 63: 357-363.

For a sophisticated discussion of the probablistic movement of searching animals — and for a good bibliography of further reading on the topic — see F. Bartumeus and S.A. Levin (2008) Fractal reorientation clocks: linking animal behavior to statistical patterns of search. PNAS 105: 19072-7.

Erratic and unpredictable behavior is reviewed in the book P.M. Driver and D.A. Humphries (1988) Protean Behaviour: the Biology of Unpredictability.

For a review of the (several) genetic mechanisms by which T. Brucei varies its armor, see J.E. Taylor and G. Rudenko (2006) Switching trypanosome coats: what’s in the wardrobe. Trends in Genetics 22: 614 – 620.

And for an account of somatic hypermutation in the immune system, see a text on immunology, such as the one by J. Kuby, T.J. Kindt et. al. (2006).

A good list of articles on the evolution and maintenance of sex can be found here.

Only the very primitive will attempt to kill roaches with shoes and/or other objects intended to smash them. Among other things, if one is successful in killing the roach one often has a smashing [sic] mess embedded in the paint/wallpaper for which the cures are expensive and time consuming.

The more evolved roach killer utilizes a couple or three other solutions. The first is those great roach traps that hold nasty food they can take back to their nests and kill all the other roaches for you.

The second is to use a glass to trap the roach (this is very easy and works regardless of which direction the roach uses on takeoff), spray an ammonia based window cleaner beside the glass, then move the glass with roach over the ammonia. S/he’ll die in short order.

If you’re forced to trap him/her on the wall, the third solution is to slide a piece of cardboard under the glass, take him/her outside to release and stomp.

Aaron Hirsch may have made up the part about prey giving the impression that it is infected, but maybe he hasn’t seen a possum under threat. It’s true that sometimes they “play dead” but the young ones I tried to roust from my garbage can instead showed all the symptoms of terminal illness: sluggish twitching, gaping, rolling, defecating, eyes half-closed. As soon as I dumped them — careful not to touch — at the edge of the lawn, they recovered remarkably and positively dashed away into the long grass.

Precision and variability are equally important, depending on what sort of environment you live in. A highly variable environment favors organisms that can respond variably, while a very stable environment favors precision. If humans always struck from the same direction, we might see roaches that always scurried in the same direction. Of course, our way keeps things interesting.

You can generally kill a fly–if you don’t mind getting your hands messy–by clapping your hands directly above and slightly behind the little guy. When threatened from above the fly almost always takes off in a backward slant.

The story of the cockroach selection of escape routes is an excellent example of the application of the “mixed strategy” concept of game theory. A mixed strategy is a selection from a specified number of alternatives by a probability rule and is a mathematical expression of deception and bluffing. The definition of randomness in the notes is correct but incomplete. Unfortunately our brains are wired for deterministic solutions and thus the difficulty for acceptance of the mixed strategy concept. Mutations are obviously nature’s response to protect against adverse changes in the environment and thus optimize the chances for survival.

It occurs to me that randomizing foraging behavior may have played a role in the evolution of religion. If you consult the village shaman about where to hold today’s hunt and she consults a cow’s shoulder-blade to get the answer, the hunting is going to proceed on a pretty random basis. That way, you avoid over-hunting some areas and optimize your chances of finding food. The groups that randomize best survive to pass on the meme. Eventually you end up with a tradition of blessing the foxhounds and praying for rain and have hymns especially written for the purpose.

Perhaps the concept of entropy would help bring the themes of the essay into sharper focus. We associate randomness with entropy, whereas living organisms represent the antithesis of entropy. So it is somewhat surprising and paradoxical to see Nature harness randomness here and there in her designs for order.

Conversely, we might ask: Is there anything other than randomness and entropy at work in the wholesale extermination of species? Or more broadly: in view of his effect on the biosphere, is the overall contribution of man to the planet one of decreasing or increasing entropy?

Antibodies do not need to exhibit a “perfect” fit for the antigens to which they bind in the course of mediating immunity. In fact, the notion of perfect fit should play no role in discussions of antibody structure and function, as the concept is incoherent in the context of the principles of physical chemistry, such as thermodynamics, that pertain to explanations of antibody affinity and specificity. Perfect fit of antibodies to antigens is essentially a pre-Darwinian concept, even though antibodies were not discovered until well after the publication of “On the Origin of Species.”

The distinction between somatic hypermutation of antibody variable region genes and mutation elsewhere in the genome is not as sharp as suggested. Most mutations of antibody variable region genes are also harmful (i.e. result in diminished function).

Cockroaches and humans share the characteristic of being generalist species: pretty good at a lot of things and fitting into a lot of places and not really good at one thing or place, like the hummingbird mentioned in the column.

Most species intensively utilize their particular ecologic niche, which is why when environments change rapidly, species die-off is common. Generalist species prefer extensive utilization of resources over intensive. Generalists would rather move to a better location than get better at what they do in their present location, which is how anatomically modern humans managed to colonize the globe so quickly. It also explains suburbs and exurbs.
Proponents of dense urban core cities are fighting against the current of human nature. If humans preferred to live that densely, there would be more than one New York City.

There are advantages to imperfect adaptation. The randomness of the cockroach’s spin move is paralleled by the behavior of NBA centers playing down in the post. Both increase unpredictability and thus survival.

The desire for humans to move is at the heart of our society. There would be no United States without its history of massive immigration, and the idea that humans under stress can be effectively stopped from moving is hopeless. Politicians like to play off that theme, but even extreme control of borders, as in the case of the present day Gaza Ghetto, shows that borders will always be porous. It is part of who we are in the core of our being.

I think that you leave out the role that chance plays in the environment that surrounds each organism that takes part in evolution. Most evolving occurs in a process called punctuated equilibrium — long periods of stability marked by a rapid and fundamental change in the environment, creating a surrounding in which the organism that survived in the stable environment is no longer viable, and in which a randomly mutated organism is better suited for survival.

Yes, this is an example of natural selection harnessing the randomness of mutations; but let’s not forget that randomness in the physical environment plays a huge role in promoting randomness on an individual, or species, level.

Without going into much detail, there are staggering similarities between what you describe in this article and many of the more ‘effective’ (for lack of a better word) computer viruses. You’ve probably already seen that spam is slightly randomized to try and slip past adaptive filters, but a more interesting parallel can be drawn between real biological viruses and polymorphic computer viruses. Some of these make use of ‘genetic programming’, whereby the virus will alter its own makeup, what it does and how it works. This is usually done pseudo-randomly and makes detection very difficult. I think you might find the parallels between the biological and computer science theory usage of randomness to be very interesting — I certainly do!

For years, researchers have referred to the phenomenon described in cockroaches as “anticipation,” as in anticipatory systems. The cockroach is not reacting–hence probability is the wrong term to apply and that is why scientists will never be able to predict its movement. It is using its anticipatory capabilities–the range of POSSIBILITIES open to it. This might sound like the cockroach is “reasoning.” It is not, since anticipation (or what Benjamin Libet described as “readiness potential”) has been proven to occur milliseconds before the act, which can even be reversed within those milliseconds. The cockroach, like birds, has all the brains it needs.

It is time for scientists to take a look into the existing work in anticipatory systems–the “new frontier” in science.

Feral cats are often described as being unadoptable due to a fear of humans – a fear that is instinctual as humans are often of ill – intent. I have noticed though that this is not always true. It seems to be that feral cats cover the spectrum of very fearful (you hardly ever see them as they don’t come out when humans are about and flee from any kind of contact) , moderately cautious (they will let you feed them but avoid any close contact), and very friendly (they will attempt to adopt you by following you and even walking into your house). During the Middle Ages in Europe when killing cats was very popular fearful cats survived better – these days its a mixed bag as you have both cat loving humans and sadististic ones (from evil kids to guys looking for bail animals to train their pit bulls on). Since evolution only cares for the species and not the individual having a mixed response allows better for the surviival of the species.

As far as bug control ever since I adopted a stray cat that is a manaic when it comes to devouring food all the bugs from my apartment have vanished – – they must have had a conference and decided to flee for as long as “Lucky” is in residence.

Cockroach escape behavior has been deciphered a long time ago at Cornell. See the works of Camhi, Heetderks and the likes. The elusive cockroach has two “tails” with hairs arranged in patterns such that only subsets of them pivot in response to wind puffs incident from different angles, thus triggering fourteen giants neurons (seven on each tail) to fire in mathematically clustered patterns, each pattern distinct from the others depending on the wind angle of attack.

“And evidently, among some species of prey, the response to an oncoming predator is to do as much unpredictable, weird and pointless stuff as possible, increasing the probability that the attacker will a) be totally confused, b) decide that messing with such a crazy character is too risky…”
This works with humans, too: back in college a girlfriend of mine was being followed by an unsavory guy who kept making suggestive comments. She put her finger in her nose, whirled around, and flourished a booger at him: “Come on,” she yelled. “Come and get it!” He fled.
Similarly, I know a fellow who startled an intruder late at night in his office. This guy’s about 5 feet 5 and 130 pounds soaking wet, so he decided his best chance was to act crazy. He start spouting gibberish while laughing loudly. Again, the intruder fled.
I’m practicing my crazy dance in case I ever need to defend myself….

When killing a house fly, I make use of the knowledge that flies are able to track motion but are not sophisticated enough to track two motions.

What I do is slowly wave my left hand and get the fly focussed on that left hand, then I kill the fly with the swatter in my right hand. This method yields a much higher success rate than with just one hand.

Sex isn’t for us — it’s for our genes. In fact, life isn’t for us. Life is about genes reproducing themselves; we and other animals and plants just happen to be the machines they create in order to get themselves reproduced.

In fact, the very fact that we enjoy sex is the result of our genes building into our brains a way of rewarding us with drugs when we perform actions crucial to copying those genes. In effect we are given a drug addiction at puberty so that we will do their bidding.

Those interested in this topic may want to read The Selfish Gene, an outstanding book by Richard Dawkins.

Another term for this is ‘protean behavior’. Evolutionary psychologist Geoffrey Miller writes: “Humphries and Driver (1970) termed this sort of adaptively unpredictable behavior “protean behavior”, after the mythical Greek river-god Proteus, who eluded capture by continually, unpredictably changing form. Their book Protean behavior: The biology of unpredictability (Driver & Humphries, 1988) presents a detailed theory and many ethnological observations. Though they did not cite game theory, they made analogies between protean behavior in animals, unpredictable feints in human sports, and randomizing methods in military strategy…..Along with directional fleeing, protean escape behaviors are probably the most widespread and successful of all behavioral anti-predator tactics, being used by virtually all mobile animals on land, under water, and in the air.”ftp://all.repec.org/RePEc/els/esrcls/prote.pdf

Why was my suggestion on how to dispose of a roach any less acceptable than any of the other blogs? Granted, my approach may be a little unorthodox but no less effective than the approches proffered by those whose blogs you published and certainly no less humane if that was the issue. Squishing, swatting, stomping, trapping, and poisening whole roach colonies can’t possibly be more humane or effective than what I found to be effective. Also, the other blogs concerning how to dispose of a roach weren’t anywhere near as humorous as mine. Of course I understand the article was not about disposing of roaches but about the relationship between randomness and natural selection in nature. Still, my blog was funnier.

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Olivia Judson, an evolutionary biologist, writes every Wednesday about the influence of science and biology on modern life. She is the author of “Dr. Tatiana’s Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex.” Ms. Judson has been a reporter for The Economist and has written for a number of other publications, including Nature, The Financial Times, The Atlantic and Natural History. She is a research fellow in biology at Imperial College London.